Surgical stents have long been known which can be surgically implanted into a body lumen, such as an artery, to reinforce, support, repair or otherwise enhance the performance of the lumen. For instance, in cardiovascular surgery it is often desirable to place a stent in the coronary artery at a location where the artery is damaged or is susceptible to collapse. The stent, once in place, reinforces that portion of the artery allowing normal blood flow to occur through the artery. One form of stent which is particularly desirable for implantation in arteries and other body lumens is a cylindrical stent which can be radially expanded from a first smaller diameter to a second larger diameter. Such radially expandable stents can be inserted into the artery by being located on a catheter and fed internally through the arterial pathways of the patient until the unexpanded stent is located where desired. The catheter is fitted with a balloon or other expansion mechanism which exerts a radial pressure outward on the stent causing the stent to expand radially to a larger diameter. Such expandable stents exhibit sufficient rigidity after being expanded that they will remain expanded after the catheter has been removed.
Radially expandable stents come in a variety of different configurations to provide optimal performance in various different particular circumstances. For instance, the United States patents to Lau (U.S. Pat. Nos. 5,514,154, 5,421,955, and 5,242,399), Baracci (U.S. Pat. No. 5,531,741), Gaterud (U.S. Pat. No. 5,522,882), Gianturco (U.S. Pat. Nos. 5,507,771 and 5,314,444), Termin (U.S. Pat. No. 5,496,277), Lane (U.S. Pat. No. 5,494,029), Maeda (U.S. Pat. No. 5,507,767), Marin (U.S. Pat. No. 5,443,477), Khosravi (U.S. Pat. No. 5,441,515), Jessen (U.S. Pat. No. 5,425,739), Hickle (U.S. Pat. No. 5,139,480), Schatz (U.S. Pat. No. 5,195,984), Fordenbacher (U.S. Pat. No. 5,549,662) and Wiktor (U.S. Pat. No. 5,133,732), each include some form of radially expandable stent for implantation into a body lumen.
One problem encountered in the use of radially expandable surgical stents is the difficulty in precisely determining the position of the stent both before, during and after it is implanted and expanded. Typically, stents are formed from stainless steel or a nickel titanium alloy. These materials are not readily perceptible when medical imaging devices, such as fluoroscopes are used to view the site where the stent has been implanted. To enhance the radiopacity of surgical stents, it is known in the prior art to provide a radiopaque marker on the stent which is clearly identifiable when a fluoroscope or other imaging device is used. Such radiopaque stents taught in the prior art have suffered from a number of drawbacks. For instance, many radiopaque markers restrict the ability of the stent to expand radially, protrude from the surface of the stent in a potentially harmful manner, fail to provide a complete outline of the extent of the stent, or illuminate so brightly on an imaging device that fine details such as blood vessels and other bodily structures are obscured in the images obtained.
One such radiopaque marker stent is the subject of European Patent Application No. 95302708.3 published on Nov. 2, 1995. The radiopaque stent markers identified in this European patent application utilize plating techniques to plate a band of radiopaque material to portions of the radially expandable stent. The radiopaque stent markers disclosed in this European patent application significantly enlarge the thicknesses of the elements adjacent where the plating occurs, making this technique significantly less effective on stents sized for implantation in smaller body lumens. If a lesser plating thickness is utilized, insufficient radiopaque material is added to provide the desired radiopacity. Other drawbacks of the radiopaque stent markers of this European patent application include that the plating material can become detached from the stent, especially when the plating material is gold and the stent is made of stainless steel. Also, such plated stents must be masked on both outer and inner surfaces. The masking procedure is difficult to accurately perform, especially on inner surfaces of stents with small diameters.
Accordingly, a need exists for a radially expandable stent featuring radiopaque markers which can be utilized on stents of all different sizes, does not interfere with the expansion of the stent and provides a clear image on a fluoroscope or other medical imaging device. Such a stent with radiopaque markers should additionally be configured in a manner facilitating its manufacture using known manufacturing techniques and commonly utilized implantation materials.